DE102010056580B4 - Arrangement for the evaporation of liquid natural gas - Google Patents

Abstract

The aim of the invention is to overcome the disadvantages of known technologies for re-evaporation of LNG by a new arrangement and to decouple usable high-quality electrical energy, so that a positive energy and operating cost balance results. For this purpose, a clockwise power plant process is arranged in a chain for heating and evaporation of the LNG with a circulating working fluid between ambient temperature and the temperature of the liquid and to be evaporated natural gas, wherein the upper temperature level of the power plant process is defined by the atmosphere.

Description

The invention relates to an arrangement with heat exchangers for the evaporation of large mass flows of liquefied natural gas, which is also referred to as LNG (liquefied natural gas), and was liquefied for the purpose of transport and intermediate storage and at atmospheric pressure, depending on the proportion of methane in the liquid state, a temperature of about -161 ° C has.

The natural gas, after evaporation in heat exchangers which constitute at least part of the apparatus, is fed as superheated steam into a network pressure pipeline.

The two sides of the wall of at least one heat exchanger, referred to as heat exchanger walls, on the one hand with the to be evaporated cold liquid natural gas, the LNG, in contact, which should therefore be referred to as LNG side, and on the other side with the heating fluid in contact, which should therefore be referred to as Heizfluidseite.

The liquid natural gas (LNG) is brought to high pressure by means of pumps and then evaporated by the supply of heat.

Are known arrangements in which a portion of the liquid natural gas (LNG) is removed and this part is burned in a gas boiler, so that a heating fluid from combustion gases is present, the heat of combustion released is used as evaporation and superheat, to the remaining means Pumping high pressure liquid natural gas to overpress and overheat pumps and then inject it into the pipeline at high pressure.

In a modified embodiment of this known arrangement there is a circulating intermediate heat transfer fluid which transports the heat from heat transfer surfaces of the gas boiler to the heating fluid side.

The disadvantages in both versions are the CO2 pollution of the environment due to exhaust gases and the commercial loss of LNG, which reduces the yield of the natural gas business.

In other known arrangements, ambient heat is used for evaporation.

In this case, uses an embodiment of such a known device, the heat from surface water, which is withdrawn. The water is led directly to the Heizfluidseite, or their heat is brought by means of a circulating Zwischenwärmeträgerfluids to Heizfluidseite. The water is deprived of the necessary evaporation and superheat, which cools it down considerably.

The high pressure liquid natural gas evaporates and is overheated.

The disadvantage of the extreme water cooling on the environment of the location of such an evaporation apparatus, as well as ice formations in the vicinity of the heat extraction and heat exchange can not be excluded.

As a result, ecological habitats are changed or even destroyed.

Furthermore, it is disadvantageous that the location of the evaporation apparatus is generally located near the harbor and both water extraction and return have to be carried out remotely, which causes additional operating and capital costs.

According to patent US Pat. No. 6,945,049 B2 A technical solution is being published to convert LNG into gaseous natural gas for use on 'seagoing' vessels.

The heat source used for LNG evaporation is seawater, which is deprived of heat, causing it to cool. The heat transfer medium between seawater and LNG uses propane, which transports the heat from seawater to LNG in its own closed circuit. Propane changes its state of matter from gaseous due to heat in the evaporator in liquid due to heat dissipation in the condenser. Additionally, water vapor is used to further heat the natural gas to overheat it as needed.

The use of the patent is disadvantageously applicable only to seagoing vessels where quantities of water are unlimited. In addition, adversely, additional heat from steam is used, which is provided by burning fossil fuels or is present as waste heat on a ship. Another disadvantage is the use of seawater resistant materials for the evaporator.

Another known design uses heat from the ambient air. The air is led directly to the Heizfluidseite, or their heat is brought by means of a circulating Zwischenwärmeträgerfluids to Heizfluidseite. The ambient air is deprived of the necessary evaporation and superheat, causing it to cool strongly. In a modified embodiment of this As is known, for locations where the ambient temperature is not high enough for seasonal reasons to achieve the desired overheating temperature, a gas boiler as a reheater is additionally arranged to bring the natural gas to the desired temperature. The disadvantages are similar to those of the former known technical design, since natural gas must be burned in order to achieve the desired gas temperature.

In addition, the specific heat of the air is small, whereby large volumes of air must be conveyed through the heat exchanger, so that relatively large drive power for fans are required.

Since these heat exchangers freeze due to the precipitation of the humidity at the cold heat exchanger surfaces on the Heizfluidseite, the heat transfer is limited. Heat exchangers must therefore be taken out of service from time to time and defrosted by known methods.

For continuous operation with defrost without process interruptions parallel heat exchangers are needed, which are operated alternately to defrost and evaporate, creating additional technical effort.

The energy balance of the known designs is negative, since drive energy is required to operate the devices described and in addition natural gas must be burned.

The energy consumption for operating the pumps and fans increases the operating costs. The self-consumption of gas reduces the yield.

In the patent US Pat. No. 3,018,634 a gradual heating up to the evaporation of LNG is suggested.

The amount of heat required for this process is withdrawn, which are cooled by it. Alternatively, heat from air conditioning systems is injected. In addition, heat from ambient air is used as a heat source to overheat natural gas in a final stage. As a heat transfer fluid ethane are used for low temperatures and propane for higher temperatures in two separate closed circuits, thereby changing their state of matter of gaseous due to heat in the evaporator in liquid due to heat dissipation in the condenser. Feed pumps in the two circuits create a pressure difference between evaporator and condenser causing a temperature spread between evaporator and condenser temperatures. This allows the operation of expansion turbines in the two closed circuits and thus the extraction of mechanical energy from the process of LNG evaporation.

The disadvantage is that the operation of such a system is location-based, since heat from other processes is required. In addition, the maximum heating of the natural gas is dependent on the ambient temperature, so that at low ambient temperatures further heating to a required temperature level is required.

The patent US 4 716 237 A refers to a combination of a steam turbine whose waste heat, the heat of condensation, is used to vaporize LNG, while the shaft power of the steam turbine is used to drive a natural gas compressor.

In a mixture heat exchanger, this natural gas vapor is mixed with LNG injected through a plurality of nozzles so that an intense heat exchange between natural gas vapor and sprayed LNG takes place and LNG completely evaporates to natural gas. To raise the temperature of this mixture, the cold natural gas is compressed in a compressor to higher pressure, whereby the temperature rises.

Two other patents with the numbers US 4 231 226 A and US Pat. No. 3,992,891 describe plants for LNG evaporation, which consists of a combination of compressors, expansion turbines and heat exchangers, which belong to a closed fluid circuit in which a separate working medium is used, whose state of aggregation does not change in the circulation. According to US Pat. No. 3,992,891 is used as the working medium air. For the operation of these plants external high temperature heat in the heat exchanger in front of the gas turbine is required, according to US Pat. No. 3,992,891 1200 K are given. The turbine drives the compressors and, depending on the level of waste heat, generates excess mechanical power that drives a generator.

From a thermodynamic point of view, it only makes sense to use mechanical work to generate mere heat for heating natural gas - as in the patents US 4 716 237 A . US 4 231 226 A and US Pat. No. 3,992,891 suggested - if an external waste heat sources can be tapped. The need-based location selection of waste heat is a serious disadvantage

Otherwise, additional heat must be generated, which requires raw materials, causes operating costs and pollutes the environment.

The invention has the object to eliminate these disadvantages by a new arrangement and to decouple usable high-quality electrical energy, so that there is a positive energy and operating cost balance.

The object is solved with the features of claim 1.

Advantageous embodiments are given in the claims 2 to 6.

According to the invention, evaporation and overheating of the LNG are realized in at least three substeps, each using different technologies of their own.

The three subsystems of the device according to the features of the invention are communicatively connected on the LNG side and are flowed through by the LNG in succession.

The device according to the features of the invention uses in the first partial step, the temperature difference between ambient temperature and extremely low temperature of the liquid natural gas for generating mechanical energy by means of a power plant process. The mechanical energy can advantageously be used to generate electricity, and thus fed into the grid. The low temperature level of the liquid natural gas LNG is the heat sink compared to the ambient temperature.

The first subsystem is characterized by components that form a clockwise force process, with a temperature upper heat exchanger, which is acted upon by the heat from the environment, whereby the working fluid is brought to near ambient temperature and thus increases its volume, a An expansion device for decoupling the mechanical energy, for example by means of a turbine, in which the working fluid is expanded from the pressure in the upper heat exchanger to a lower pressure, and the expanded working fluid is cooled in a temperature-lower heat exchanger by the cold liquid natural gas, and means are provided for increasing the pressure with which the working fluid from the pressure in the lower heat exchanger to the pressure in the upper heat exchanger, which corresponds approximately to the inlet pressure of the turbine, is brought.

As working fluids can be substances with and without change of state when passing through the cycle components.

A cycle in which the working fluid passes from steam to liquid and back to steam as it passes through the cycle components is known as Clausius-Rankine Prozes.

Another cycle process without changing the state of matter when passing through the cycle components is the Brayton process.

However, the invention is not limited to these two processes.

With regard to maximum energy yield, the cyclic process with state change is advantageous.

The first subsystem therefore has an evaporator, which is acted upon by the heat from the environment, whereby the working fluid is evaporated, a turbine in which the working fluid from the evaporator pressure to the lower condenser pressure is released, including means for cooling with condensation of the expanded working fluid are through which the cold liquid natural gas flows, so that the steam is completely converted into liquid due to condensation, and a feed pump, with which the working fluid is brought to evaporating pressure.

The evaporator is heated with ambient air. The condenser is cooled with liquid natural gas, which itself heats up. The rise in temperature results from the heat balance between the available heat of desiccation and condensation of the cycle and the heat required to heat the LNG.

As a result, the heat of condensation in the first section to the heating fluid side of the LNG heat exchanger is delivered to the LNG and also mechanical work is decoupled.

As a working fluid advantageously fluids are used whose critical temperature is greater than the condensation temperature. The heat source temperature of the environment may also be above the critical temperature. In addition, the choice of fluids must also consider the component availability.

Possible working fluids would be, for example, tetrafluoromethane (CF ₄ , also known as refrigerant R14) or methane (CH ₄ , also known as refrigerant R50), but the invention is not limited thereto.

A device according to the features of the invention uses in a second sub-step of the invention ambient heat from the air as a heat source for evaporation and overheating of the LNG, wherein the heat from the environment to the Heizfluidseite in an advantageous embodiment means a volatile heat transfer fluid, z. As propane, with the state changes condensation on the Heizfluidseite the LNG heat exchanger and evaporation at the heat source of the air-heat exchanger according to the principle of a heat pipe is transported, so that the pressure differences for transporting the volatile heat transfer fluid only overcoming of flow resistance and geodetic pressures within serve this section.

A device according to the features of the invention uses in a third sub-step a heat pump, which is designed as a left-handed cyclic process consisting at least of evaporator, compressor, condenser and expander, wherein the evaporator ambient heat from the air and the capacitor receives heat to the Heizfluidseite the LNG Heat exchanger supplies.

Advantageously, the device parts in the second and third sub-step according to the invention use the same fluid, for. For example propane.

The second and third substeps are advantageously arranged in an integrated subsystem. The invention is not limited thereto.

The integrated subsystem thus includes heat pipe and heat pump.

The heat pipe and heat pump use the same working or circulating fluid.

The subsystem is characterized by a single liquid container for the working fluid and a single air heat exchanger. From the lower bottom part of the liquid container liquid refrigerant is conveyed by circulation pump to the air-heat exchanger to evaporate there.

The steam returns to the top of the liquid container. The head of the liquid container is connected on the one hand by means of pipeline to the intermediate heat exchanger, where the circulating fluid condenses and passes through the liquid return back into the liquid container. The head portion of the liquid container is on the other hand connected to the suction line of the compressor, which sucks the working fluid and compressed to a higher pressure, so that the condensation temperature in the post-heat exchanger is high enough to the natural gas as desired, for. B. to + 2 ° C to heat.

The working fluid is liquefied by this heat release. It runs over a liquid line and a regulated throttle point, for example a float valve, also high-pressure float, back into the liquid container.

The device according to the invention uses only ambient heat from the air for re-evaporation of the LNG.

As a result, the individual heat exchangers, depending on the arrangement in the system with respect to the natural gas to be evaporated different temperature differences, since the temperature of the natural gas to be evaporated (heat sink temperature) from -161 ° C to + 2 ° C.

The formation of ice from moisture in the air is accepted in known solutions.

In an advantageous arrangement of the heat exchanger as a function of the heat sink temperature ice formation on the heat exchanger surfaces is avoided in that the heating of the natural gas is carried out in stages in stages and the heat exchanger are arranged accordingly.

On heat transfer surfaces with wall temperatures on the air side below -60 ° C precipitated moisture from the air does not adhere, so that defrosting of ice formations is not required in this temperature range.

The energy balance of the arrangement according to the invention is positive, since drive energy can be decoupled and fed into a network without having to burn natural gas.

The energy required for the operation of ancillary equipment, such as the feed pump and blower for the heat exchanger is covered free of charge.

The arrangement according to the invention gives a positive energy and operating cost balance.

The invention will be explained in more detail by the examples.

Figure 1 shows evaporation and overheating of the LNG in three steps.

Figure 2 shows a pressure, enthalpy diagram with the state changes of the working fluid for the three sub-steps of natural gas heating according to the invention.

Figure 3 shows a pressure, enthalpy diagram with the state changes of the working fluid for the clockwise cycle with process temperatures

Figure 1 shows a simplified circuit diagram according to the invention. Evaporation and overheating of liquid natural gas, LNG, will be in three Partial steps, in the right-handed steam power process 1 , the pump circuit 2 , the heat pump cycle 3 realized, each of which uses different technologies.

The three subsystems of the device are according to the features of the invention on the LNG side through the LNG pipe run 13 communicating connected and are flowed through by the LNG successively.

The first subsystem uses the temperature difference between the ambient temperature and the temperature of the liquid natural gas to generate mechanical energy by means of a power plant process.

The first subsystem, the right-handed steam power process 1 , has a LT evaporator 4 which is acted upon by the heat from the environment, whereby the working fluid is evaporated, a turbine 7 , in which the working fluid from the evaporator pressure to condenser pressure is released. The condensation heat in the LT capacitor 9 for cooling and condensation of the expanded working fluid is discharged to the cold liquid natural gas on the LNG side. The steam is converted to liquid, and the feed pump 8th promotes the working fluid with evaporation pressure to the LT evaporator 4 where the working fluid is re-evaporated.

Also the LT-evaporator 4 is heated with ambient air. The LT capacitor 9 is cooled with liquid natural gas, which heats itself. The rise in temperature results from the heat balance between the available heat of desiccation and condensation of the cycle and the heat required to heat the LNG.

As a result, the heat of condensation in the first section becomes the heating fluid side of the LNG heat exchanger in the LT condenser 9 delivered to the LNG, and also mechanical work on the turbine 7 decoupled. The working fluid used is R14, whose critical temperature is greater than the condensation temperature. The heat source temperature of the environment at R14 is also below the critical temperature.

The second subsystem, the pump cycle 2 , has two heat exchangers, the MT evaporator 5 and the MT capacitor 11 , and the circulation pump 10 ,

The heat exchanger, the MT evaporator 5 It extracts heat from the ambient air while the circulation fluid evaporates. The heat is circulated fluid to the heat exchanger, the MT capacitor 11 , transported where it condenses. The circulation pump 10 Press the liquid again to the MT evaporator 5 ,

The cycle is closed.

The third subsystem, the heat pump cycle 3 , has a HP evaporator 6 which extracts heat from the ambient air because the evaporation temperature is kept below the ambient temperature as the working fluid evaporates. The working fluid is in the HP compressor 14 compressed to higher pressure, reducing the condensation temperature in the WP capacitor 12 rises above ambient temperature. This allows the natural gas to be heated to the desired temperature.

After liquefaction, the working fluid at the HP throttle point 15 relaxed again to evaporation pressure. The cycle is closed.

In Figure 2, the state changes of the working fluid for the three sub-steps of natural gas heating according to the invention are plotted from bottom to top.

The steam power process is the right-handed cyclic process 21 , also the pump circuit 22 is a right-handed process during the heat pump process 23 is going around left.

Figure 3 shows the pressure, enthalpy diagram for the working fluid methane with the state changes of the working fluid for the steam cycle with process temperatures and enthalpy changes and for the natural gas to be heated (LNG) whose specific heat content is equated to the working fluid methane for reasons of simplification.

Point 34 illustrates the LNG enthalpy at 90 bar and -161 ° C before heating. The warming of the LNG is due to the heat of dewatering and condensation depending on the outside air temperature to the point 35 or 35a realized.

Point 35 shows the LNG enthalpy at 90 bar after the first partial step at outside temperature -10 ° C during point 35a the LNG enthalpy at 90 bar and outside temperature + 30 ° C shows.

The steam cycle is shown for two extreme outdoor temperatures, which cause the working fluid to evaporate in the evaporator down to -20 ° C or up to + 20 ° C under high pressure under certain conditions, which are not further explained here. The pressure increase 49 From 35 bar to about 90 bar of condensate (methane in liquid phase) takes over the feed pump 8th , By supplying heat from the ambient air, which cools down, the state change follows fluid heating 48 at air temperatures of about -10 ° C to -20 ° C or the state change fluid heating 48a at air temperatures from approx. + 30 ° C to + 20 ° C. The working fluid evaporates. The relaxation of the steam in the turbine results in a mechanical work that is used to generate electrical energy. This is followed by the state change of desuperheating and condensation 46 for relaxation of -20 ° C or the change in state of desuperheating and condensation 46a at relaxation of + 20 ° C. The LNG warming 31 is caused by the heat of desiccation and condensation 32 applied when relaxed from -20 ° C or LNG heating 31a is caused by the heat of desiccation and condensation 32a applied when relaxed from + 20 ° C.

This will raise the LNG enthalpy and point 35 after first partial step at outside temperature -10 ° C, while at outside temperature of + 30 ° C the point is reached 35a is reached.

The energy balance of the arrangement according to the invention is positive, since drive energy can be decoupled and fed into a network without having to burn natural gas.

The energy required for the operation of ancillary equipment, such as the feed pump and blower for the heat exchanger is covered free of charge.

The arrangement according to the invention gives a positive energy and operating cost balance.

In addition, the environment is relieved by power generation without primary energy.

LIST OF REFERENCE NUMBERS

1

right-handed steam power process

2

Pump circulation

3

Heat pump cycle

4

LT-evaporator

5

Heat exchanger, MT evaporator

6

WP-evaporator

7

turbine

8th

feed pump

9

LT-capacitor

10

circulating pump

11

Heat exchanger, MT capacitor

12

WP-capacitor

13

LNG pipe section

14

WP-compressor

15

WP-throttle point

21

right-handed cycle

22

Pump circulation

23

heat pump process

31

LNG heating in the first step

32

Dewatering and condensation heat

32a

Dewatering and condensation heat

33

expansion work

33a

expansion work

34

LNG enthalpy at 90 bar and -161 ° C

35

LNG enthalpy at 90 bar after the first partial step (outside temperature -10 ° C)

35a

LNG enthalpy at 90 bar after the first partial step (outside temperature + 30 ° C)

44

LNG enthalpy at turbine exit at -20 ° C steam inlet temperature

44a

LNG enthalpy at the turbine outlet at + 20 ° C steam inlet temperature

45

Isotherm for -20 ° C

45a

Isotherm for + 20 ° C

46

Change of state of desuperheating and condensation

46a

Change of state of desuperheating and condensation

47

Change of state fluid-relaxation (expansion work)

47a

Change of state fluid-relaxation (expansion work)

48

Change of state Fluid heating

48a

Change of state Fluid heating

49

Pressure increase by means of a feed pump 8th

Claims (6)

Arrangement with heat exchangers for the evaporation of large mass flows of liquefied natural gas (LNG), characterized in that the heat exchangers each have working fluid sides and LNG sides and the LNG sides from the inlet of the cold liquefied natural gas downstream form an order firstly belonging to a condenser of a clockwise one Power plant process, which also has evaporator, turbine and feed pump, secondly associated with a pump circuit, which also has a further heat exchanger and a circulation pump, and third belonging to a condenser of a left-hand refrigeration circuit, which is a heat pump by its configuration, and also at least one evaporator , has a compressor and a throttle point and that ambient air is the heat source of the clockwise power plant process, the pump circuit and the left-handed refrigeration cycle. Arrangement according to claim 1, characterized in that the heat exchanger within the rechtsläufigen power plant process on its working fluid side, the lower temperature level of the power plant process represents that the heat exchanger within the pump circuit on the working fluid side of the pump circuit is the lower temperature level and that the heat exchanger within the refrigeration cycle on the working fluid side of the left-hand cycle represents the upper temperature level and forms the capacitor. Arrangement according to claim 1 and 2, characterized in that as working fluid in the clockwise power plant process, a fluid is present with phase change, which condenses at lower temperature level of the power plant process, that as a working fluid within the pump circuit, a fluid with phase change is present, which condenses at the lower temperature level, and that within the refrigeration cycle there is a fluid with phase change that condenses at the upper temperature level. Arrangement according to claim 3, characterized in that as working fluid in rechtsläufigen power plant process natural gas, methane or tetrafluoromethane are present. Arrangement according to claim 1 to 4, characterized in that as the working fluid within the pump circuit and that within the refrigerant circuit, the same fluid is present. Arrangement according to claim 1 to 5, characterized in that as working fluid propane is present.

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